The present invention relates to forklift truck load push devices and push-pull devices (hereinafter collectively referred to by the term "push-pull"). More particularly, the invention relates to improvements enabling such devices to utilize the standard forks of the lift truck to support the load, and enabling the forks to be mountable and demountable relative to the lift truck carriage in unison with the push-pull device, without necessitating excessive forward protrusion of the push-pull device in its fully-retracted condition.
Previous forklift truck push-pull units fall into several different categories. In one category are standard push-pull attachments such as that shown in Brudi U.S. Pat. No. 3,640,414, or those manufactured by Cascade Corporation of Portland, Oregon under the designations 3OC and 45C, or those manufactured by Long Reach Manufacturing Division of Anderson Clayton Company. All of these have push-pull assemblies comprising a frame, a push plate and a push-pull linkage extending therebetween consisting either of horizontally pivotable or vertically pivotable pantographic-type links. Each of these devices also has a transverse member at the bottom of its frame for detachably mounting different types of special-purpose load-supporting members. Because of their attachment to the bottom of the frame, the load-supporting members can be mounted, demounted and side shifted relative to the lift truck carriage in unison with the push-pull assembly However, the expense of such standard push-pull units is relatively high, partially because such units cannot utilize the standard forks of the lift truck to support the load but rather must be provided with their own special loadsupporting members capable of attachment to the transverse member at the bottom of the push-pull frame.
Another category of push-pull slipsheet handlers includes those which are mountable on the lift truck carriage while the standard forks remain mounted on the carriage. Examples of such devices are shown in Anderson, Jr., U.S. Pat. No. 3,885,692, Rocco U.S. Pat. No. 4,065,012, Farmer, et al., U.S. Pat. No. 4,482,286 and Frison U.S. Pat. No. 4,619,579. However, in these structures the forks are not mountable and demountable relative to the lift truck carriage in unison with the push-pull assembly. Nor can the push-pull assembly and forks be shifted transversely in unison relative to the lift truck carriage without the insertion of a side shifter, such as that shown in Kroupa U.S. Pat. No. 3,460,700, between the carriage and the push-pull assembly, which causes the push-pull assembly to protrude forwardly to an excessive degree thereby subtracting from the load-carrying capacity of the counterbalanced lift truck upon which the push-pull assembly is mounted.
A further prior type of push-pull device is that manufactured previously by Cascade Corporation under the designations "Model L4N" and "Model P4N," which utilized the standard forks of the lift truck as the load-supporting members while enabling mounting, demounting, and side shifting of the push-pull assembly and forks in unison relative to the lift truck carriage. The frame of the unit had an elevated transverse member of the general type employed on standard hook-type lift truck carriages from which standard forks could be suspended in a region transversely between the sides of a horizontally pivoting push-pull linkage. However the mounting of the tall, upstanding portions of the standard forks on the push-pull frame between the sides of the linkage limited the extent to which the horizontally pivoting links could be retracted, and therefore caused excessive protrusion of the push-pull assembly in its fully-retracted position thereby subtracting from the load-carrying capacity of the counterbalanced truck upon which the unit was mounted. The unit was eventually discontinued in favor of the aforementioned Cascade 30C and 45C designs which, although incapable of utilizing the standard lift truck forks, avoided the limitation on the retraction of the push-pull assembly previously caused by the upstanding portions of the standard forks.